1) Technical Field
This invention relates to resistance devices that are used to tension stationary exercise apparatus. In particular, the present invention relates to an improved and simplified centrifugal tensioning devices for stationary exercise apparatus that have a driven axle; even more specifically to bicycle trainers.
2) Background Information
The prior art on tensioning devices for bicycle trainers show various means of using disc brakes, friction plate brakes, magnetic resistance, and large and small fans for simulating wind load.
In particular the "state of the art" tensioning device for bicycle trainers is magnetic resistance and or fan resistance. Fan resistance is recognized as the best means of simulating wind load while riding. It is exponential in nature in that the faster one pedals, the more turbulence the fan causes exponentially. This was confirmed by the science editor for "Bicycling Magazine" Chester R. Kyle, PH.D. (P.76 December 1990 Issue of "Bicycling"). The drawback to fan resistance is noise. At 25 miles per hour a fan or wind trainer can generate over 80 decibels, a problem if you want to listen to music or watch TV or live in a thin walled apartment.
Magnetic resistance is quieter, producing about 60 decibels at 25 mph. However, MAGS are less realistic than fans because their resistance increases in direct proportion to speed, rather than exponentially. (P.70 December 1990 issue of BICYCLING magazine). Therefore, magnetic resistance does not simulate actual bicycle riding conditions. Another drawback to magnetic resistance is the high number of moving parts needed to manufacture one unit. This high number of moving parts makes magnetic resistance expensive to manufacture and undependable because of break-down. The more moving parts the more potential for wear and breakdown. After about two years of use they tend to get noisy and need to be rebuilt.
The challenge was to design and build a resistance unit that provided the same exponential resistance as the fan, but, without the noise. The challenge was also to design a resistance unit that had few moving parts and was therefore inexpensive to manufacture and also one that provided variable resistance according to the level of the user and one that was also adaptable to any type of stationary exercise unit and also dependable.
A prototype was built of the subject invention and attached to the roller of a rear mount bicycle trainer for demonstration and testing purposes. The present invention made very little noise and the tension was directly related to the rate of speed of the driven axle; as the rate of speed of the driven axle increased, the tension increased exponentially, like the fan. It was found that the amount of tension could be varied by shifting the gears of the bicycle which either increased or decreased the speed of the rotatable shaft which in turn affected the centrifugal force acting on the radially moveable braking material. Increased speed caused the centrifugal force to increase which increased the friction of the braking material acting against the fixed cover. Clutch plate cork from the auto industry was found to be ideal braking material showing little wear and was inexpensive and easily replaceable. This high density cork also made no noise.
For stationary exercise equipment where gearing is not present, the means to vary the centrifugal resistance can be added. This can be accomplished by any known means by those skilled in the art; additional axially moveable braking material can be released from more slots, weight of the braking material can be varied and means to increase or decrease the rotational speed of the driven axle can be accomplished by adding different sized pulleys, effectively simulating the different rotary transmission means of a bicycle. Adding weight to the braking material increases the resistance. These and other ways of changing the resistance of the centrifugal tensioning device can be added by any known means by those skilled in the art. The more feed back the better, so the state of the art exercise machines utilize electronic sensors to detect heart rate, pulse, time, speed, cadence and computers to save previous work-outs etc. The centrifugal tensioning device can be adapted to work with and be controlled by these types of electronic feed-back devices by those skilled in the art.
Studies have shown that an RPM of between 60-80 RPM with a power output of 300 watts or roughly 24 miles per hour to be optimal. Heart rate, VO2 blood lactate levels, rate of perceived exertion and gross efficiency all seem to be at their optimal levels at 80 RPMs. Studies have also shown that as power output goes up so should the cadence. For instance, for track racing and sprint distance racing, an RPM of 110 appears to be optimal.
The challenge was to find the right combination of number and size of slots to house the correct weight and size of the braking material to provide ample variations in tension to the conventional bicycle trainer. Various sizes of rings, slots and braking material were experimented with to find the right combination of size, number and weight of material to provide enough tension based upon power output and RPMs to satisfy the work-out demands of both the casual rider and the professional racer.
There are five variables to work with in combination with a driven shaft; the size of the slotted ring, the number of slots, the kind of-braking material, the weight of the braking material and the speed of the driven rotatable shaft. It was found that a 21/2" outside diameter ring 1/2" wide with four slots sized to house 1/4" by 1/2" cork braking material when attached to a 1.3" rotating axle was ideal for a bicycle trainer with a multi-speed 26"-27" bicycle attached to it. Simple 1/2 inch deep drill holes positioned every 90 degrees around the ring were found to work effectively to house the braking material in the cavity formed by a simple drill bit.
For those skilled in the art, there are many size combinations that would work depending on the amount of tension desired on a particular exercise apparatus. A sixth variable comes into play on exercise devices that require a pulley system for hook up, such as rollers as illustrated in FIG. (5). The size of the pulley ring directly effects the speed of the slotted ring.
A by-product of friction is heat. It was found that during use, the friction cover got quite hot. To dissipate the heat, the cover can be manufactured in such a way by those skilled in the art to perform both as a friction cover and a heat dissipating means. This is accomplished by having radial grooves on the outer surface of the cover to help dissipate the heat and having a smooth inner surface to act as a friction surface. The high density cork was found to be an excellent non heat conductive material. It was found that while the friction cover got hot, the slotted ring which spins within the cover with ample clearance never got hot and the high density cork braking material did not transfer the heat. Teflon rod also worked and worked well against steel, noiselessly, while the cork worked well with the aluminum. Further research into graphite glass and Kevlar composites used in the heavy equipment braking industry proved to resist wear better and the higher coefficient of friction added more resistance. A suitable braking material has a high coefficient of friction and is wear resistant at 10-15,000 RPM's and withstands high heat.